The present invention generally relates to a pipeline and more particularly, to an improved joint construction of a pipeline of exhaust pipes or the like which are provided with flanges at each end thereof so as to be coupled with each other by using fastening members.
Generally, in a conventional exhaust system of an engine for a motor vehicle, as shown in FIG. 1, there has been employed an exhaust passage including an engine a, an exhaust manifold b, an exhaust pipe c, an exhaust pipe d having a catalytical converter g, an exhaust pipe e, and an exhaust pipe f having a muffler h, which are connected with each other in the above order from the engine a to the exhaust pipe f so as to purify the exhaust gas from the engine a and muffle the exhaust noise during discharge of the exhaust gas into the atomsphere. Generally, flanges c1 to f1 have been provided at each end of the exhaust pipes c to f so as to be coupled with each other, at the coupling portions A to D of the exhaust pipes c to f, with the use of fastening members comprising bolts and nuts.
In the conventional arrangement as described above, however, the surfaces of the flanges c1 to f1 have been directed at right angle with the centerline or axis of the pipeline (exhaust pipe c to f) and to be parallel with each other, so that the tightening of the bolts and nuts is required to be performed from the direction in parallel with the centerline of the pipeline. Meanwhile, since the exhaust pipes c to f are provided below a floor i, with a shielding plate j for heat shielding and the protection of the exhaust system being disposed below and in the vicinity of said exhaust pipes c to f, the coupling operation as described above has usually been performed obliquely from below the car body, using an impact wrench with a universal joint type socket. However, in the coupling operation as described above, the direction for tightening the bolts and nuts is different from the direction of operating the impact wrench, so that the universal joint portion has been apt to be damaged owing to a large load applied thereto, thus increasing the expenses required for tools due to the short service life. Moreover, the large rotational vibration of the socket during the tightening has caused mechanics to suffer from tendovaginitis, while deterioration in working efficiency and increased cost of labor have resulted because the nuts are required to be temporarily mounted on the bolts before the tightening. Furthermore, there have been dangers that mechanics may be injured by falling bolts or get burnt by exhaust pipes c to f at high temperatures when loosening the tightened portions with the impact wrench.